Abstract

Due to its high electrical conductivity and excellent transmittance at terahertz frequencies, graphene is a promising candidate as transparent electrodes for terahertz devices. We demonstrate a liquid crystal based terahertz phase shifter with the graphene films as transparent electrodes. The maximum phase shift is 10.8 degree and the saturation voltage is 5 V with a 50 µm liquid crystal cell. The transmittance at terahertz frequencies and electrical conductivity depending on the number of graphene layer are also investigated. The proposed phase shifter provides a continuous tunability, fully electrical controllability, and low DC voltage operation.

(a) The THz pulse intensity through the sample holder, the bare glass substrate, single layer, bi-layer, tri-layer, and 4-layer graphene films. The each data set is shifted in time. (b) The transmittance of single layer, bi-layer, tri-layer, and 4-layer graphene films at THz frequencies. (c) The absorption rate of each additional stacked layer of graphene film. (d) Sheet resistance of CVD graphene films versus the number of stacked graphene layers.

(a) THz pulse signal transmitted through the phase shifter with different bias voltages. The inset shows the waveform of the THz signal in the full scanning range. Single layer graphene is used. (b) Voltage controlled phase shifts at different frequencies.